This invention relates to gas-discharge lamps. In this context, it relates to the specific field of gas-discharge lamps for dielectrically inhibited discharges, i.e. gas-discharge lamps in which the electrodes, or in any case at least the anodes, are isolated by a dielectric layer from the gas filling for the discharge.
Such gas-discharge lamps for dielectrically inhibited discharges have most recently become the subject of increased attention because they are able to exhibit various technical properties due to which they appear to be suitable, above all, as flat radiating elements for backlighting liquid crystal screens. The present invention does not primarily relate to this field of application and is also not restricted to flat radiating elements.
In the vast majority of cases, gas-discharge lamps for dielectrically inhibited discharges have electrode arrangements with a multiplicity of electrodes for producing a multiplicity of spatially distributed partial discharges. In flat radiating elements, this is used to backlight a surface expanse as uniformly as possible, for example.
This invention is based on the technical problem of developing gas-discharge lamps for dielectrically inhibited discharges with a view to increasing the options for application and use.
The invention solves this problem by means of a gas-discharge lamp having a discharge vessel which is filled with a gas filling, has a multiplicity of electrodes and has a dielectric layer between at least one anode part of the electrodes and the gas filling, wherein the electrodes are divided into separately operable groups for independently switchable operation.
It also relates to a traffic light as claimed in claim 8, a display device or signal lamp as claimed in claim 9 and an interior light as claimed in claim 10.
The basic concept of the invention thus involves, with a multiplicity of electrodes in a gas-discharge lamp for dielectrically inhibited discharges, dividing the electrodes into groups that can be operated in electrical isolation, that is to say making it possible for some of the anodes and/or some of the cathodes to be driven separately in electrical terms, and similarly making it possible for the other or some more of the cathodes and/or anodes to be electrically driven in the same way, but independently of the first ones. This produces electrode groups for independently switchable operation, with cathodes and anodes in one group being allocated to one another in terms of spatial arrangement, so that they can develop discharges amongst one another. The division into groups can be based on the electrical isolation of cathodes or anodes or on interaction between an electrical isolation of the cathodes and one of the anodes.
At this point, and in the following text, the terms anode and cathode should moreover not be understood as being restricted to unipolar operation. For bipolar operation of the electrodes, there is no difference between anodes and cathodes in this respect, so that respective statements for anodes or cathodes are valid for both xe2x80x9celectrode typesxe2x80x9d in the bipolar case.
In this context, the invention preferably relates to so-called flat radiating elements. In the case of these, a discharge volume is formed from plates, for example made of glass, which are not necessarily planar in the sense of straight, but are areal and largely planar, with the electrode structures being produced on one or both glass plates. The distribution of electrodes over a large surface and possibly the use of additional diffuser layers allow flat lamps with a large surface and very uniform distribution of light to be produced. Areal production of light is an essential feature in many applications. These may involve backlighting a surface having a particular expanse or distributing a particular light power onto a surface in order to reduce the dazzling effect. An areal configuration may also be important for reasons of aesthetic design or for reducing the formation of shadows.
The invention may be particularly advantageous in just such flat radiating element applications, particularly if, according to a preferred embodiment, the groups that are to be operated independently correspond to different luminous surfaces. The luminous surfaces are then to be operated independently of one another, therefore, the luminous surfaces still being part of the same gas-discharge lamp, that is to say in particular of the same discharge vessel. Examples are advertising panels, in which various graphical elements are operated independently of one another, for example some flashing and some permanently illuminated.
A further example is signal lamps, whose different graphical elements correspond to the electrically isolated groups. In this case, it may be important to increase the conspicuousness, as is also the case for the advertising surfaces already mentioned. Alternatively, the symbolization of particular incorporated meanings may be involved, for example through successive activation of various luminous surfaces showing a continuous arrow movement or the like. A further possibility is the use of various, alternatively selectable luminous surfaces having different meanings for matching the meaning of one and the same signal lamp to various situations.
In the context of display devices, in the field of advertising as well, or signal devices, it is furthermore preferable to adapt the electrode geometry to match the respective surface shape to be backlit by an electrode group. According to this, the corresponding electrode group then essentially xe2x80x9cfillsxe2x80x9d the relevant luminous surface, but does not go far beyond this into regions which do not need to be backlit at all. With regard to this feature, reference is made, by way of addition, to European Patent Application 97 122 799.6 from the same applicant, entitled xe2x80x9cFlxc3xa4chstrahler mit xc3x6rtlich modulierter Flxc3xa4chenleuchtdichte [Flat radiating element with locally modulated surface luminous intensity]xe2x80x9d.
Preferred shapes for an electrode geometry adapted in this manner are, particularly in the case of technical display devices, circular, circle-segment-shaped, annular or annular-segment-shaped surfaces. These are found in many analog displays. Reference is also made to the second exemplary embodiment.
Within the scope of the invention, there is no need whatsoever for the electrode groups which can be operated in electrical isolation to correspond to locally separate luminous surfaces as well. Hence, it may also be advantageous according to the invention to interleave two or more electrode groups that can be operated in electrical isolation within one and the same luminous surface such that each of the electrode groups can backlight the luminous surface substantially uniformly. By doing this, it is possible to produce, by way of example, a function similar to a dimmer function (in addition to such a function, as well), in that operating individual electrode groups with different powers or particular combinations of electrode groups makes the same luminous surface appear with different luminous intensities.
In particular, this allows (discrete) brightness reduction without the circuit complexity of a dimmer function. It is sufficient to separate the electrode groups and a corresponding switching device for selectively supplying individual groups or a number of the groups, in which case the power of the electronic ballast need not be controllable. Alternatively, it can be worthwhile to combine this technology with a dimmer function. This is because it has been found that, during dimming, that is to say when the power of an electronic ballast is reduced, problems can occur in the range of, in comparison to the rated power, very low powers. In this respect, using the fact that individual electrode groups can be switched separately, as described above, and using an additional dimmer function which, however, covers only one power range in the vicinity of the respective rated power of an electrode group, it is possible to find a worthwhile combination which can be dimmed down a long way, too, by disconnecting groups.
There may naturally also be cases in which there is neither uniform backlighting of the same luminous surface by different separate electrode groups nor are there actually separate luminous surfaces for separate electrode groups, which are nonetheless part of the invention.
A further possible application for locally separate electrode groups consists in using special optical films or similar devices to provide the. separate luminous surfaces for the electrode groups with different radiation directions or at least direction focal points, so that, on the whole, switching operation over between the electrode groups can change the radiation properties of the lamp in terms of direction as well.
The invention also relates to certain particularly interesting exemplary applications. Firstly, the invention relates to a traffic light in which the groups that can be operated in electrical isolation each correspond to one of the signal surfaces, although the overall traffic light contains only one standardized gas-discharge lamp. In this case, different luminescent materials can be used to produce the corresponding colors for the signal surfaces within the same gas-discharge lamp. With regard to preferred luminescent materials for this application and for other applications in the field of signal lamps, reference is made to the European application xe2x80x9cSignallampe und Leuchtstoffe dazu [Signal lamp and luminescent materials therefor]xe2x80x9d from the same applicant, with the file reference 97122800.2. As regards the physical shape of the traffic light lamp, reference is made, by way of addition, to the European application xe2x80x9cFlache Signallampe mit dielektrisch behinderter Entladung [Flat signal lamp with dielectrically inhibited discharge]xe2x80x9d from the same applicant, with the file reference 97122798.8.
Furthermore, the invention is specifically directed at signal lamps in vehicles, ships or airplanes and at display devices in them. Reference is made to the first exemplary embodiment. Motor vehicle rear lights, warning lights on operation panels etc. are also conceivable, however.
Finally, the invention also relates to an interior light in which the advantages of the invention can be used on the one hand for aesthetic reasons or on the other hand for regulating the luminous intensity.